Ethanol vs. Biodiesel

A new study from the university of Minnesota comparing the lifecycle energy costs and emissions of corn ethanol to soy biodiesel is all over the press this morning.

The results are no surprise to any of us who follow the industry: corn ethanol yields 25% more energy than it takes to produce it; while soy biodiesel yields 93% more.

The numbers for ethanol ar not new: people have been arguing about the EROEI (Energy Return on Energy Invested) for ethanol for years, and the numbers have slowly risen with improving technology from about -10% to today’s 25%. What are new, are the EREOI numbers for soy biodiesel. I had only heard one number for the EREOI of “biodiesel” before – and no mention of the feedstock was made, nor was I able to trace it back to a reputable source… I suspect it was a back of the envelope calculation by a biodiesel advocate. That number was a 220% return, quoted to me twice, once by management at Blue Sun Biodiesel, and once by the person manning the booth for the International Center for Appropriate and Sustainable Technology, both of whom do good work, but who have an incentive to believe this highest number they hear. Disclaimer: I too have an incentive to believe the highest number I hear because I have a Jeep that I use biodiesel in to minimize my carbon emissions. Using the new numbers, my Jeep Liberty has about the same carbon footprint as my 2002 Prius, when running on B100. On B20, which I use in the winter, the Prius still looks much better. I’m pining for a plug-in hybrid diesel.

But I’m very happy to see reality injected into the whole biofuels debate. Neither ethanol not biodiesel (nor both together) is going to save the US from having to import petroleum: if our entire corn and soybean output were shifted to these biofuels, that would only replace about 12% of gasoline demand, and 6% of diesel demand… are we ready to start talking about massively investing in increasing the efficiency of our vehicles yet?

One other new note in the article, which I like given my affection for biodiesel, is that soy is a much less fertiliser intensive crop than corn, and so growing it has fewer local environmental impacts. I hope these authors continue their work, and expand the study to include other feedstocks for both ethanol (sugarcane, cellulostic) and biodiesel (canola, algae, recycled oil).

[…] of the well-to-wheels Energy Return on Energy Invested (EREoI) for biodiesel range from about 1.93and up, depending on the feedstock, although few numbers are available. The most commonly quoted […]